The invention relates to screens used to filter and control solids, such as screens used to remove solids from drilling mud used in drilling wells such as hydrocarbon wells. More specifically, the invention relates to a design for fluids directional and re-directional system for use with screens and flow direction, preferably with diagonal or other flexible ribs which reduces the build-up of solids on particular areas of the screen, which build-up would otherwise reduce flow rate and increase the propensity of the screen to tear or rip.
The need for solids control, such as in conjunction with the use of drilling mud in hydrocarbon well drilling, has long been known in the prior art. Drilling mud, typically a mixture of clay and water and various additives, is pumped through the hollow drill string (pipe, drill collar, bit, etc.) down into the well and is ejected through holes in the drill bit. Among other functions, the mud picks up cuttings (rock bits) and other solids from the bottom of the well and carries these solids away from the bit as the mud is pumped upward and out of the well in the space between the well walls and the drill string. At the top of the well, the solids-laden mud is directed to the shale shaker, a device consisting essentially of a series of screens which catch and remove the solids from the mud as the mud passes through the screens. As indicated in FIG. 1, each screen is caused to vibrate by vibratory equipment generally shown by the indicator 100 in such a manner as to create a longitudinal flow of trapped solids in either direction on the top surface of the screen for removal and disposal of the solids. This filtering, along with other cleaning processes, allows the mud to be reused.
The fineness or coarseness of the mesh of a screen may vary depending upon such factors as flow rate and the size of the solids to be filtered by the screen. The finer the mesh, the higher is the propensity of the screen to tear. Referring now to the drawings, this propensity to tear is further increased by the tendency of solids trapped by the screen 1 to laterally migrate (by the vibration of the screen) to and congregate at the lowest part of the screen 1, which is suspended as shown in FIG. 1. It is virtually impossible to hang a screen 1 so that the lateral plane of its surface is perfectly horizontal; rather, either the center 5 of screen 1 bulges upward laterally from the longitudinal edges 2 of screen 1 as shown in FIG. 2, in which case the screen is said to be xe2x80x9cover slungxe2x80x9d, or the center 5 bulges downward as shown in FIG. 3, in which case the screen 1 is said to be xe2x80x9cunder slungxe2x80x9d. If screen 1 is over slung (FIG. 2), solids tend to congregate at the longitudinal edges 2; if screen 1 is under slung (FIG. 3), solids tend to congregate at center 5.
Screen 1 may comprise a single layer or, as shown in FIGS. 2, 3, 5, and 6 for illustration, two or more layers, the bottom screen layer 9 having a coarser, stronger mesh to provide support for one or more top screen layers 10 which are primarily responsible for the solids filtering function. Top screen layer(s) 10, being of a finer mesh, is the more prone to tearing.
As a means to limit screen tearing and to otherwise strengthen and support screen 1 and to hold screen layers 9 and 10 together, it is known in the prior art to construct screens with flexible ribs 6 of polypropylene or similar material. As shown in FIG. 1, these ribs 6, which generally vary in width from {fraction (3/16)} inch to {fraction (5/16)} inch, generally comprise a set of longitudinal ribs 7 running the entire length of screen 1 paralleling longitudinal edges 2), and shorter lateral ribs 8 running between and perpendicular to adjacent longitudinal ribs 7, spaced at regular intervals. Each set of lateral ribs 8 running between the same two longitudinal ribs 7 is staggered with adjacent sets of lateral ribs 8, thereby creating a brickwork pattern of ribs 6. Ribs 6 are of approximately the same thickness as the screen 1 itself (approximately 0.036 inch) and enclose the full thickness of both bottom screen layer 9 and top screen layer(s) 10. The intersecting of longitudinal ribs 7 and lateral ribs 8 create panels 11 of screen; a tear in top screen layer(s) 10 beginning in any particular screen panel 11 is prevented from spreading to adjacent screen panels 11 by the ribs 6 that form the edges of the panel 11 in which the tear occurs.
A different, superior pattern of ribs 6 is also known in the prior art which counteracts the tendency of trapped solids to flow laterally to the lowest parts of a suspended screen. See U.S. Pat. No. 4,820,407, to Kenneth Lilie, issued Apr. 11, 1989. It reduces the incidence of screen tearing, increases the filtering surface area of the screen, and enhances the longitudinal flow of trapped solids across the top surface of the screen.
Reference numerals 2, 3, 4 and 100 and the parts thereof have the same meaning for FIGS. 4-6 as they do for FIGS. 1-3. As indicated in FIGS. 4-6, screen 1 has edges 2 connected to hooking clasp 3. Hooking clasps members are engaged by clamps 4 to vibratory equipment generally shown by the reference numeral 100. Referring now to FIG. 5, the pattern of ribs 6 comprises a single longitudinal center rib 12 extending the full length of screen 1 and, on either side of center rib 12, a set of diagonal ribs 13. Each set of diagonal ribs 13 comprises a series of equally spaced and parallel diagonal ribs 13, each rib 13 beginning laterally at the longitudinal edge 2 corresponding to such set of diagonal ribs 13 and extending diagonally to center rib 12. (At the lateral edges 14 and 15 of screen 1, some diagonal ribs 13 are cut off before actually reaching longitudinal edges 2 or center rib 12 or imaginary extensions thereof, but otherwise are situated the same as and are parallel to full diagonal ribs 13.) For each diagonal rib 13 of one set of diagonal ribs 13, there is a corresponding and mirroring diagonal rib 13 of the other set of diagonal ribs 13, beginning at the other longitudinal edge 2 and extending diagonally and laterally in the same longitudinal direction and ending at the same point on center rib 12 as its corresponding diagonal rib 13 of the other set of diagonal ribs 13. The thickness of ribs 12 and 13 is greater than the thickness of screen 1 (whether comprising a single layer-or multiple layers), and so in addition to fully enclosing the thickness of bottom screen layer 9 and top screen layer(s) 10, ribs 12 and 13 are slightly raised above the top surface of screen 1, such as 0.007 inch above said surface. (Optionally, the entire screen 1 may be bordered with ribs 6 of like construction in order to strengthen the screen 1.)
Screen 1 is intentionally either over slung (FIG. 5) or under slung (FIG. 6). If screen 1 is over slung, then, referring to FIG. 4, the longitudinal flow of trapped solids is directed over the top surface of screen 1 from the far lateral end 14 longitudinally of screen 1 to the hear lateral end 15. Because ribs 12 and 13 form a slightly raised barrier in relation to top screen layer(s) 10, diagonal ribs 13 tend to cause trapped solids to move laterally from longitudinal edges 2 to center 5 of screen 1, thereby counteracting the tendency of solids to congregate at longitudinal edges 2 of an over slung screen (FIG. 5). If, on the other hand, screen 1 is under slung, then, again referring to FIG. 4, the longitudinal flow of trapped solids is directed from near lateral end 15 of screen 1 to far lateral end 14, in which case diagonal ribs 13 tend to cause trapped solids to move laterally from center 5 to longitudinal edges 2, thereby counteracting the tendency of solids to congregate at center 5 of an under slung screen (FIG. 6).
The pattern of the screen in U.S. Pat. No. 4,820,407 under field tests shows that the pattern of screen 1 (in most cases) does exhibit the tendency for the mud to be directed along the diagonal rib pattern toward the center of the screen.
Further, all models of hooked type shale shaker equipment normally have rib rail reinforcements positioned on the screen beds for the existing equipment. One purpose these ribs serve is to support the screen panel size span as it becomes engaged in a vibrating action to perform the function of screening or separating. These ribs are normally made of steel, run the length of the screen bed, and are reinforced with differing substances to cushion the screens underside from the metal rib.
During normal operation of the shale shaker, the cushion reinforcement will wear due to the effects of the equipment""s vibrating motion. As this reinforcement wears, it leaves an impression in the screen and will eventually cause the screen to wear if the reinforcement wears unevenly or becomes brittle and cracks, or wears out, leaving the underside of the screens surface resting against the metal ribs. If the cushion reinforcement methods are not changed on a regular basis, the associated screen life will be detrimentally affected.
The invention comprises an improved fluids directional and redirectional system used in conjunction with filtering screens of any type, such fluids directional and redirectional system being directed towards the discharge end of the screen. Such fluids directional and redirectional system may also be in the center of the screen or may have a combination of both types. The screen may be comprised of two opposing sets of raised directional diagonal ribs of various lengths, each set of various lengths comprising series of equal or unequally spaced and parallel ribs. The screen may have raised director ribs of various lengths disposed along the screen.
The raised, spaced apart director ribs may be spaced apart from each other along any angle of a screen to permit gates to exist between the channeling ribs. These director ribs may then be spaced such that the next adjacent director ribs to gate or opening are across the flow path for that gate or opening.
The screens may also have a rib rail cushion support within the screen body, formed by plastic melted and laminated into the screen assembly at the points in the screen surface where the impact points of the rib rail reinforcements of the shale shakers will make contact with the rib rail cushion of the screen.